A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

A

ACGIH - American Conference of Governmental Industrial Hygienists

acute - occurring over a short period of time; used to describe brief exposures and effects which appear promptly after exposure

acute exposure - a single exposure to a toxic substance or microorganism which results in severe biological harm or death. Acute exposures are usually characterized as lasting no longer than a day.

algae - microscopic plants which contain chlorophyll and live floating or suspended in water. They also may be attached to structures, rocks or other submerged surfaces. They are food for fish and small aquatic animals. Excess algal growths can impart tastes and odors to potable water. Algae produce oxygen during sunlight hours and use oxygen during the night hours. Their biological activities appreciably affect the pH and dissolved oxygen of the water.

algal bloom - sudden, massive growths of microscopic and macroscopic plant life, algae, and cyanobacteria, which develop in lakes, reservoirs, and marine waters

algicide - any substance or chemical specifically formulated to kill or control algae

allergen - something that causes an allergy, allergic response, or hypersensitivity

allergy - an exaggerated or inappropriate immune response initiated by exposures to antigens such as mold spores, pollen, or certain drugs and foods

ambient - environmental or surrounding conditions

amplification - (amplification source) the process of indoor growth leading to an increased indoor microbial concentration compared to the immediate outdoor environment 

anaphylaxis - (anaphylactic shock)  a severe and life-threatening allergic reaction. These rare reactions can occur following exposure to biological or chemical antigens  such as microbes, insect stings, drugs, and even certain types of foods.

anion - a negatively charged ion in an electrolyte solution, attracted to the anode under the influence of a difference in electrical potential. Chloride (CI-) is an anion.

antagonism - interference or inhibition of the effect of one chemical by the action of another chemical

antibodies - proteins in the blood that are generated in reaction to foreign proteins or polysaccharides; also called "immunoglobulins" 

Anderson sampler - a sieve-type air sampling device that uses a vacuum pump to draw air through a radial pattern of 300 small holes, impacting particles in each of the small streams of air onto the surface of microbial growth medium. 

antigen - a substance or molecule that is recognized by the immune system. The molecule can be from a foreign material such as bacteria or viruses.

antihistamine drugs - group of drugs that block the effects of histamine, a chemical released in body fluids during an allergic reaction.  These drugs may reduce itching, sneezing, and runny nose.

aspergillosis - a group of diseases caused by the fungus Aspergillus; affected tissues may include lungs, bronchial airways, sinus cavities, ears, and eyes

asthma - an immediate hypersensitivity (allergy) resulting in respiratory symptoms such as wheezing, coughing, shortness of breath, and a feeling of constriction within the chest or bronchial airways

autotroph - an organism that can produce its own food from inorganic molecules and sunlight. All photosynthetic plants are autotrophs.

B

B cells - small white blood cells crucial to the immune defenses; also known as B lymphocytes, they come from bone marrow and develop into blood cells called plasma cells, which are the source of antibodies

background level - the average presence of a chemical substance or microorganism in the environment, originally referring to naturally occurring phenomena

bacteria - microorganisms with prokaryotic cell organization (lacking membrane-bounded nucleus and other specialized features); bacteria are also typically much smaller than fungi (molds)

bioaerosol - an airborne dispersion of particles containing whole or parts of biological entities, such as bacteria, viruses, dust mites, fungal hyphae, or fungal spores 

biocide - substances such as antibiotics, bacterialcides, or fungicides that are capable of destroying living organisms 

biochemical oxygen demand (BOD) - the amount of oxygen consumed by microorganisms (mainly bacteria) and by chemical reactions in the biodegradation of organic matter

black water - liquid and solid human body waste and the carriage water generated through toilet usage

blastomycosis - a disease caused by the fungus Blastomyces dermatitidis; may infect lungs, skin, mucous membranes, bones, internal organs, and joints 

bronchitis - an inflammation of the bronchi (lung airways), resulting in persistent cough that produces consideration quantities of sputum (phlegm)

bronchodilator drugs - a group of drugs that widen the airways in the lungs

brown-rot fungi: fungi that are capable of utilizing the cellulose and hemicellulose portions of wood but are incapable of decomposing brown lignin; rot characteristics include crumbly appearance and brown coloration 

BRI - building-related illness: a recognized disease that can be attributed to airborne building bioaerosols or chemical pollutants

C

CFUs - Colony Forming Units; individual regions of growth attributed to a single reproductive unit such as a spore or vegetative cell

carcinogenic - cancer-producing or cancer-causing

carriers - seeminglyly healthy people who harbor disease-causing microbes in the body and who can infect others by passing the microbes on to them

cation - a positively charged ion in an electrolyte solution, attracted to the cathode under the influence of a difference in electrical potential. Sodium ion (Na+) is a cation

cell - the smallest and most fundamental unit of life

central nervous system - portion of the nervous system which consists of the brain and spinal cord; CNS

chlorination - The application of chlorine to water, generally for the purpose of disinfection, but frequently for accomplishing other biological or chemical results (aiding coagulation and controlling tastes and odors)

chlorine demand - Chlorine demand is the difference between the amount of chlorine added to water and the amount of residual chlorine remaining after a given contact time. Chlorine demand may change with dosage, time, temperature, pH, and nature and amount of the impurities in the water. Chlorine Demand, mg/L = Chlorine Applied, mg/L - Residual, mg/L

chlorine requirement - The amount of chlorine which is needed for a particular purpose. Some reasons for adding chlorine are reducing the number of coliform bacteria (Most Probable Number), obtaining a particular chlorine residual, or oxidizing some substance in the water. In each case a definite dosage of chlorine will be necessary. This dosage is the chlorine requirement.

chronic - occurring over a long period of time, either continuously or intermittently; used to describe ongoing exposures and effects that develop only after a long exposure

chronic exposure - long-term, low-level exposure to a toxic chemical or microorganism

coccidioidomycosis - a disease caused by the fungus Coccidioides immitis; may infect lungs, internal organs, bones, joints, and skin 

colony - a discrete growth usually discernable by the naked eye; this term is usually used in reference to growth originating from a single spore or cell

contact dermatitis - a rash or inflammation of the skin caused by contact with biological or chemical substances. The reaction may be an immunologic response or a direct toxic effect of the substance. Among the more common causes of a contact dermatitis reaction are detergents, metals, chemicals in rubber gloves and condoms, certain cosmetics, plants such as poison ivy, and topical medications.

corticosteroid drugs - a group of anti-inflammatory drugs similar to the natural corticosteroid hormones produced by the cortex of the adrenal glands. Among the disorders that often improve with corticosteroid treatment include asthma, allergic rhinitis, eczema and rheumatoid arthritis.

cryptococcosis - a disease caused by the fungus Cryptococcus neoformans; may infect lungs, central nervous system, skin, and lining of body cavity 

cytotoxin - a chemical compound that is poisonous to cells

D

DNA (deoxyribonucleic acid) - a complex molecule found in the cell nucleus which contains an organism's genetic information

decomposition - the conversion of chemically unstable materials to more stable forms by chemical or biological action. If organic matter decays when there is no oxygen present (anaerobic conditions or putrefaction), undesirable tastes and odors are produced. Decay of organic matter when oxygen is present (aerobic conditions) tends to produce much less objectionable tastes and odors.

degradation - chemical or biological breakdown of a complex compound into simpler compounds

dermal exposure - contact between a microorganism (or chemical) and the skin

dermatophytes - a fungus that causes skin disease in humans or other animals

Der p 1 - an allergen found in house dust mite droppings. A common cause for irritations and allergic reactions usually attributed to dust.

dew point - the temperature at which water would condense from the air if the air mass were cooled. In general, when the relative humidity is high, the dew point will be close to the air temperature. At 100% relative humidity, the dew point is equal to the air temperature. When the relative humidity is low, the dew point is much lower than the air temperature.

diatom - unicellular algae capable of photosynthesis and characterized by producing a thin outer shell made of silica (glass)

dinoflagellates - a diverse assemblage of biflagellate unicellular organisms, which constitute an important component of marine, brackish, and fresh bodies of water

disease - a state in which a function or part of the body is no longer in a healthy condition

dose-response - a quantitative relationship between the dose of a chemical or microorganism and an effect caused by the chemical or microorganism

dose-response curve - a graphical presentation of the relationship between degree of exposure to a chemical or microorganism (dose) and observed biological effect or response

dust mite - a house dust mite (Dermatophagoides pteronyssinus), sometimes abbreviated by allergists to HDM, is a small insect that is a common guest in human habitation. The dust mite droppings are the most common cause of allergic rhinitis and asthma on this planet � they contain an allergen that can irritate a person, or cause an allergic reaction.

E

endotoxin - a lipopolysaccharide component of the membrane of gram-negative bacteria that is heat stable and toxic; a secreted toxin produced by bacteria is termed an "exotoxin"

epidemic - a widespread outbreak of a disease, or a large number of cases of a disease in a single community or relatively small area. Disease may spread from person to person, and/or by the exposure of many persons to a single source, such as a water supply.

epidemiology - a branch of medicine which studies epidemics (diseases which affect significant numbers of people during the same time period in the same locality). The objective of epidemiology is to determine the factors that cause epidemic diseases and how to prevent them.

eutrophication - the increase in the nutrient levels of a lake or other body of water; this usually causes an increase in the growth of aquatic animal and plant life

exposure assessment - the determination or estimation (qualitative or quantitative) of the magnitude, frequency, duration, route, and extent (number of people) of exposure to a chemical or microorganism

extrapolation - estimation of unknown values by extending or projecting from known values

extrinsic asthma - asthma that is triggered by an allergic reaction, usually something that is inhaled

F

fecal coliform bacteria - bacteria found in the intestinal tracts of animals. Their presence is an indicator of pollution and possible contamination by other pathogens.

FEV1 - the forced expiratory volume (FEV) in 1 second - the amount of air blown out in the first second, means how much someone can breathe out in one second, trying as hard as possible.

FEV6 - the forced expiratory volume (FEV) in 6 seconds is how much someone can breathe out in six seconds, trying as hard as possible.

FVC- the forced vital capacity (FVC) - the maximum volume of air that can be forcibly expired from the lungs.

flagellates - microorganisms that move by the action of tail-like projections

free available residual chlorine - that portion of the total available residual chlorine composed of dissolved chlorine gas cl2), hypochlorous acid (HOCl), and/or hypochlorite ion (OCl-) remaining in water after chlorination. This does not include chlorine that has combined with ammonia, nitrogen, or other compounds.

fungus - (pl. fungi) a kingdom of organisms (equal in rank to the Plant Kingdom or the Animal Kingdom) defined technically as a parasite or saprobeic, filamentous or single-celled eukaryotic organism, devoid of chlorophyll and characterized by heterotrophic growth, and the production of extracellular enzymes.  Fungi include yeasts, molds, mildews, and mushrooms.  

fungicide - a chemical compound capable of inhibiting or destroying the growth of fungi

G

gastroenteritis - an inflammation of the stomach and intestine resulting in diarrhea, with vomiting and cramps when irritation is excessive. When caused by an infectious agent, it is often associated with fever.

genes - units of genetic material (DNA) that carry the directions a cell uses to perform a specific function

genus - a grouping of similar species according to taxonomic criteria, for example, humans (Homo sapiens) belong to the genus 'Homo' and the species 'sapiens'

H

HVAC - Heating, Ventilating, and Air-Conditioning

HEPA filter - High Efficiency Particulate Air filters that have been tested to assure removal of 99.9% of particles 0.3 �m in size. Another benefit of a HEPA air filtration system is that it can remove harmful V.O.C.'s (Volatile Organic Compounds) which are gases that come from house-hold chemicals and synthetic materials.
HEPA filters are highly recommended for allergy sufferers. HEPA filters collect the airborne dust and dander including dust mites rather than just pushing the air around the room as an ionizer does. Many filtration systems that don't have HEPA filters leave the toxic elements trapped in the room and eventually they become airborne again. The idea is to remove the dust from your home, not simply move it from here to there.

hepatotoxin - a chemical compound that is poisonous to the liver

hepatitis - hepatitis is an inflammation of the liver usually caused by an acute viral infection. Yellow jaundice is one symptom of hepatitis.

heterotrophic microorganisms - microorganisms that use organic matter synthesized by other organisms for energy and growth

heterotrophic plate count (HPC) - the number of colonies of heterotrophic bacteria grown on selected solid media at a given temperature and incubation period, usually expressed in number of bacteria per milliliter of sample

histamine - a chemical present in cells throughout the body that is released during an allergic reaction. Histamine is one of the substances responsible for the symptoms of inflammation and is the major reason for running of the nose, sneezing, and itching in allergic rhinitis. It also stimulates production of acid by the stomach and narrows the bronchii or airways in the lungs.

histoplasmosis - a disease caused by the fungus Histoplasma capsulatum; may infect lungs, skin, mucous membranes, bones, skin, and eyes

host - an individual who is parasitized or infected by a parasite or pathogen

human health risk - the likelihood (or probability) that a given exposure or series of exposures may have or will damage the health of individuals experiencing the exposures

human immunodeficiency virus (HIV) - the virus that causes AIDS

humus - organic portion of the soil remaining after prolonged microbial decomposition

hypersensitivity - an allergy; an exaggerated or inappropriate immune response categorized based on which part of the immune system that is involved and the onset of response (i.e. Types I, II, III, IV)

hypha - (pl. hyphae) a branching tubular structure that forms the vegetative body of a growing filamentous fungus

hypochlorite - chemical compounds containing available chlorine; used for disinfection. They are available as liquids (bleach) or solids (powder, granules and pellets). Salts of hypochlorous acid.

I

immune system - a complex network of specialized cells, tissues, and organs that defends the body against attacks by disease-causing microbes

immunization - vaccination or other process that induces protection (immunity) against infection or disease caused by a microbe

immunocompromised - any condition in which the immune system functions in a abnormal or incomplete manner; such conditions are more frequent in the young, the elderly, and individuals undergoing extensive drug or radiation therapy

immunoglobulins - proteins in the blood that are generated in reaction to foreign proteins or polysaccharides; also called "antibodies" 

immunosuppression - suppression of the natural immune response (see immunocompromised)

immunotherapy - ("allergy shots") is a form of preventive and anti-inflamamatory treatment of allergy to substances such as pollens, house dust mites, fungi, and stinging insect venom. Immunotherapy involves giving gradually increasing doses of the substance, or allergen, to which the person is allergic. The incremental increases of the allergen cause the immune system to become less sensitive to the substance, perhaps by causing production of a particular "blocking" antibody, which reduces the symptoms of allergy when the substances is encountered in the future.

impermeable - not easily penetrated. The property of a material that des not allow, or allows only with great difficulty, the movement or passage of water.

infection - a state in which disease-causing microbes have invaded or multiplied in body tissues

infectious diseases - diseases caused by microbes that can be passed to or among humans by several methods

inflammation - an immune system process that stops the progression of disease-causing microbes, often seen at the site of an injury like a cut. Signs include redness, swelling, pain, and heat

ingestion - type of exposure that occurs through the mouth

inhalation - type of exposure that occurs through the lungs

intrinsic asthma - asthma that has no apparent external cause

ion - an electrically charged atom, radical (such as SO₄^2-), or molecule formed by the loss or gain of one or more electrons

ionization - the splitting or dissociation (separation) of molecules into negatively and positively charged ions

J

K

keratitis - microbial infections of the cornea (eye); when caused by a fungus, it is referred to as mycotic keratitis

L

latent - present but not seen; a latent viral infection is one in which no virus can be found in the blood cells but in which those virus-infected cells can produce virus under certain circumstances

Legionnaires' Disease (Legionellosis) - a form of pneumonia caused by the bacterium Legionellae; first discovered in 1976 from infected persons attending the Legionnairs meeting in Philadelphia  

lymphocyte - any of a group of white blood cells of crucial importance to the adaptive (humoral) part of the body's immune system. The adaptive portion of the immune system mounts a tailor-made defense when dangerous invading organisms penetrate the body's general defenses.

M

malignant - very dangerous or virulent, causing or likely to cause death

mast cells - cells that play an important role in the body's allergic response. Mast cells are present in most body tissues, but are particularly numerous in connective tissue, such as the dermis (innermost layer) of skin. In an allergic response, an allergen stimulates the release of antibodies, which attach themselves to mast cells. Following subsequent allergen exposure, the mast cells release substances such as histamine (a chemical responsible for allergic symptoms) into the tissue.

meningitis - inflammation of the meninges, the membranes that surround the brain and spinal cord

microbe - a general or non-specific term for any microorganism such as bacteria, fungi (molds), algae, or protozoa

microgram (�g) - one-millionth of a gram (3.5 x 10-8 oz. 0.000000035 oz.)

micrometer (�m) or micron - a unit of length. One millionth of a meter or one thousandth of a millimeter. One micron equals 0.00004 of an inch.

microscopic - too small to be seen with the naked eye

milligrams per liter (mg/L) - a measure of concentration of a dissolved substance. A concentration of one mg/L means that one milligram of a substance is dissolved in each liter of water. For practical purposes, this unit is equal to parts per million (ppm) since one liter of water is equal in weight to one million milligrams. Thus a liter of water containing 10 milligrams of calcium has 10 parts of calcium per one million parts of water, or 10 parts per million (10 ppm).

mildew - a common name for mold or fungi; often used in reference to fungal growth on bathroom tiles and fixtures 

mixotroph - an organism capable of producing its own food from inorganic molecules and sunlight as well as feeding directly on other organisms as well

molar or molarity - a molar solution consists of one gram molecular weight of a compound dissolved in enough water to make one liter of solution. A gram molecular weight is the molecular weight of a compound in grains. For ex- ample, the molecular weight of sulfuric acid (H2SO4) is 98. A one M solution of sulfuric acid would consist of 98 grains of H2SO4 dissolved in enough distilled water to make one liter of solution.

mold - a common name for fungi that grow in a filamentous fashion and reproduce by means of spores; all molds are fungi, but not all fungi are considered 'molds'  

molecules - the smallest physical units of a substance that still retain the chemical properties of that chemical substance; molecules are the building blocks of a cell. Some examples are proteins, fats, carbohydrates, and nucleic acids.

most probable number (MPN) - MPN is the Most Probable Number of coliform-group organisms per unit volume of sample water. Expressed as the number of organisms per 100 mL off sample water.

motile - capable of self-propelled movement. A term that is sometimes used to distinguish between certain types of organisms found in water.

mucormycosis - a group of disease caused by the fungi belonging to the group Mucorales (Class Zygomycetes); such fungi may infect lungs, sinuses, mucous membranes, central nervous system, internal organs, and eyes 

mulch - any substance spread or allowed to remain on the soil surface to conserve soil moisture and shield soil particles from the erosive forces of raindrops and runoff

mutagenicity - the capacity of a chemical or physical agent to cause permanent alteration of the genetic material within living cells

mycellium - the collective mass of hyphae (filamentous cells) comprising the body of most fungi and molds  

mycetoma - invasive fungal infection of subcutaneous tissues (under the skin)

mycology - the scientific study of fungi (Kingdom Fungi or Mycota)    

mycosis - an infection caused by fungi (mold) (pl. mycoses)  

mycotoxicosis - any disease caused by fungal toxins (mycotoxins)  

mycotoxins - a diverse class of poisonous compounds produced by certain mushrooms and other fungi; mycotoxins are produced on the surface of mold spores and remain toxic even after the spore is dead

N

necrosis - death of cells or tissue

neoplasm - an abnormal growth or tissue, as a tumor

neurotoxin - a chemical compound that is poisonous to the nervous system

nitrification - the biological or chemical transformation of ammonium nitrogen to nitrate nitrogen

nitrogen fixation - the biological or chemical process by which elemental nitrogen, from the air, is converted to organic or available nitrogen

non-point source - pollution sources which are diffuse and do not have a single point of origin or are not introduced into a receiving stream from a specific outlet. The pollutants are generally carried off the land by storm water runoff. The commonly used categories for non-point sources are: agriculture. forestry, urban, mining, construction, dams and channels, land disposal, and saltwater intrusion.

nutrient - any substance that is assimilated (taken in) by organisms and promotes growth. For example, nitrogen and phosphorous are nutrients which promote the growth of algae. There are other essential and trace elements which are also considered nutrients.

nutrient pollution - contamination of water resources by excessive inputs of nutrients; in surface waters, excess algal production is a major concern

O

odor threshold - the minimum odor of a water sample that can just be detected after successive dilutions with odorless water. Also called THRESHOLD ODOR.

olfactory fatigue - a condition in which a person's nose, after exposure to certain odors, is no longer able to detect the odor

oligotrophic - reservoirs and lakes which are nutrient poor and contain little aquatic plant or animal life

onychomycosis - invasive fungal infections of the nail

organic - substances that come from animal or plant sources. Organic substances always contain carbon. (Inorganic materials are chemical substances of mineral origin.)

otomycosis - a superficial fungal infection of the outer ear canal

oxidation - oxidation is the addition of oxygen, removal of hydrogen, or the removal of electrons from an element or compound. In the environment, organic matter is oxidized to more stable substances. The opposite of reduction.

oxidation-reduction potential - the electrical potential required to transfer electrons from one compound or element (the oxidant) to another compound or element (the reductant); used as a qualitative measure of the state of oxidation in water treatment systems.

oxidizing agent - any substance, such as oxygen (O₂) or chlorine (Cl₂), that will readily add (take on) electrons. The opposite is a reducing agent.

ozonation - the application of ozone to water for disinfection or for taste and odor control

P

pandemics - diseases that affect many people in different regions around the world

parasites - plants or animals that live, grow, and feed on or within another living organism

particle count - the results of a microscopic examination of treated water with a special "particle counter" which classifies suspended particles by number and size

particulate - a very small solid suspended in air or water which can vary widely in size, shape, density, and electrical charge

pathogen - a microorganism that causes a disease response

periphyton - microscopic plants and animals that are firmly attached to solid surfaces under water such as rocks, logs, pilings and other structures

peak flow - the fastest rate of air (airflow) that you can blow out of your lungs. Its recorded in liters per minute (l/min).

PEF - the fastest speed a person can blow air out of their lungs.

pH - an expression of the intensity of the basic or acid condition of a liquid. Mathematically, pH is the logarithm (base 10) of the reciprocal of the hydrogen ion concentration, [H+]. pH= Log (I/[H+]) The pH may range from 0 to 14, where 0 is most acid, 14 most basic, and 7 neutral. Natural waters usually have a pH between 6.5 and 8.5.

photosynthesis - a process in which organisms, with the aid of chlorophyll (green plant enzyme), convert carbon dioxide and inorganic substances into oxygen and additional plant material, using sunlight for energy. All green plants and many microorganisms (such as algae) grow by this process.

phytoplankton - small, usually microscopic plants (such as algae), found in lakes, reservoirs, and other bodies of water

piedra - fungal infection of hair shafts resulting in the formation of dark (black piedra) or white (white piedra) nodules within the hair shaft 

plankton -1) Small, usually microscopic, plants (phytoplankton) and animals (zooplankton) in aquatic systems. 2) All of the smaller floating, suspended or self-propelled organisms in a body of water.

pneumonia - a disease characterized by the inflammation of the lungs; often caused by bacteria or certain species of fungi 

point source - a stationery location or fixed facility from which pollutants are discharged or emitted. Also, any single identifiable source of pollution, e.g., a pipe, ditch, ship, ore pit, factory smokestack.

ppb - parts per billion. Also µg/L or micrograms per liter.

ppm - parts per million. Also mg/L or milligrams per liter.

propagule - any disseminable microbial element that can give rise to new growth (e.g. spores, hyphal fragments, cells) 

pulmonary hemorrhage - a condition characterized by bleeding in the lungs caused by weakening of the lung vessels

putrefaction - biological decom- position of organic matter, with the production of ill- smelling and tasting products, associated with anaerobic (no oxygen present) conditions

Q

qualitative - descriptive of kind, type or direction, as opposed to size, magnitude or degree

quantitative - descriptive of size, magnitude or degree

R

RNA (ribonucleic acid) - a complex molecule that is found in the cell cytoplasm and nucleus. One function of RNA is to direct the building of proteins.

RAST testing - radioallergosorbent test; a blood test for measuring antigen specific antibodies (allergic reactions).  Used primarily where skin testing is impractical or unreliable (i.e. extreme sensitivity, dermatitis, children).     

reducing agent - any substance, such as base metal (iron) or the sulfide ion (S2-), that will readily donate (give up) electrons. The opposite is an oxidizing agent.

reduction - reduction is the addition of hydrogen, removal of oxygen, or the addition of electrons to an element or compound. Under anaerobic conditions (no dissolved oxygen present), sulfur compounds are reduced to odor-producing hydrogen sulfide (H₂S and other com- pounds. The opposite of oxidation.

relative humidity - an expression of how much moisture is in the air as a percentage of the total moisture the air can contain at the current temperature. For example, if the air has all the water vapor that it can contain at a given temperature, the relative humidity is 100%; if the air has only half of the vapor that it can contain at a given temperature, the relative humidity is 50%.

representative sample - a portion of material or water that is as nearly identical in content and consistency as possible to that in the larger body of material or water being sampled

residual chlorine - the amount of free and/or available chlorine remaining after a given contact time under specified conditions

respiration - the process in which an organism uses oxygen for its life processes and gives off carbon dioxide

rhinitis - an inflammation of the mucous membrane that lines the nose, often due to an allergy to pollen, dust or other airborne substances. Seasonal allergic rhinitis also is known as "hay fever," a disorder which causes sneezing, itching, a runny nose and nasal congestion.

ringworm - fungal infections of the skin resulting in raised red swellings or lines that resemble burrowing worms; includes the diseases known as athlete's foot, jock itch, and ringworm or the scalp

risk - the potential for realization of unwanted adverse consequences or events

risk assessment - a qualitative or quantitative evaluation of the environmental and/or health risk resulting from exposure to a chemical or microorganism; combines exposure assessment results with toxicity assessment results to estimate risk.

risk characterization - final component of risk assessment that involves integration of the data and analysis involved in hazard evaluation, dose-response evaluation, and human exposure evaluation to determine the likelihood that humans will experience any of the various forms of toxicity associated with a substance.

risk estimate - a description of the probability that organisms exposed to a specified dose of chemical will develop an adverse response (e.g., cancer).

risk factor - characteristic (e.g., race, sex, age, obesity) or variable (e.g., smoking, occupational exposure level) associated with increased probability of a toxic or adverse effect

risk management - decisions about whether an assessed risk is sufficiently high to present a public health concern and about the appropriate means for control of a risk judged to be significant

rotavirus - a group of viruses that can cause digestive problems and diarrhea in young children

route of exposure - the avenue by which a chemical comes into contact with an organism (e.g., inhalation, ingestion, dermal contact, injection)

S

safe - condition of exposure under which there is a "practical certainty" that no harm will result in exposed individuals

saprobe - any microorganism capable of obtaining nutrients from dead or non-living organic matter  

serology - the medical science of serum; or the technique of determining antigens or antibodies in serum

serum - the clear or slightly yellowish liquid that remains after the plasma portion is allowed to clot; blood is comprised of a plasma portion (55%) and a cellular portion (45%); plasma contains water, salts, and plasma proteins (albumin, fibrinogen, antibodies) whereas the cellular portion contains red blood cells (erythrocytes), platelets, and white blood cells (leukocytes)

Sick Building Syndrome (SBS) - a set of symptoms associated with indoor exposure to chemicals or microorganisms characterized by headaches; eye, nose and throat irritations; fatigue; and skin disorders 

sinusitis - inflammation of the membrane lining the facial sinuses (air cavities within facial bones), often caused by bacterial, fungal, or viral infection.

skin tests - tests for an allergy or infectious disease performed by a patch test, scratch test, or an intracutaneous injection of an allergen or extract of the disease-causing organism

soft-rot fungi: fungi that are capable of decomposing the cellulose and hemicellulose portions of wood; most soft-rot also partially degrade lignin; these species are most common in moist hardwoods

species - the most specific taxonomic classification; an interbreeding population of individual organisms; often abbreviated as 'sp.' in reference to a single species or 'spp.' when referencing several species

spores - reproductive units or specialized cells that provide the primary means for dispersal and survival; many fungal (mold) spores are capable of long term dormancy and are therefore referred to as resistant spores or resting spores

sterilization - the removal or destruction of all microorganisms, including pathogenic and other bacteria, vegetative forms and spores

substrate - substance on or in which a microorganism is living

surface water - all water naturally open to the atmosphere (rivers, lakes. reservoirs, streams, impoundments, seas, estuaries, etc.) and all springs. wells, or other collectors which are directly influenced by surface water

synergism - an interaction of two or more chemicals which results in an effect that is greater than the sum of their effects taken independently

T

T cells - small white blood cells (also known as T lymphocytes) that direct or directly participate in immune defenses

teratogenesis - the induction of nonhereditary congenital malformations (birth defects) in a developing fetus by exogenous factors acting in the womb; interference with normal embryonic development

teratogenicity - the capacity of a physical or chemical agent to cause teratogenesis in offspring

tissues - groups of similar cells joined to perform the same function

toxigenic -  a substance or biological entity that has the property itself or can produce one or more compounds that have the property to harm humans or other animals

total residual chlorine - the amount of available chlorine remaining after a given contact time. The sum of the combined available residual chlorine and the free available residual chlorine. Also see residual chlorine

Type I Hypersensitivity (anaphylactic reactions) - an immediate, usually localized response to allergens such as fungi, pollen, dust mites, or animal dander; examples of this type of disorder include insect stings, asthma, food allergies, drug reactions, and hives;  type of antibodies involved: IgE 

Type II Hypersensitivity (cytotoxic reactions) - a delayed response (usually within hours or days) involving reactions against antigens located on target cells which are then destroyed; examples of this type of disorder include blood transfusions reactions and hemolytic disease of newborns (involving Rh factors); type of antibodies involved: IgG, IgM

Type III Hypersensitivity (immune-complex reactions) - a delayed response (usually within hours or days) involving insoluble antigen-antibody complexes which cause tissue necrosis (death) and acute inflammation; examples of this type of disorder include Farmer's Lung (caused by fungi and other microorganisms), serum sickness, and malaria; type of antibodies involved IgG, IgM 

Type IV Hypersensitivity (cell-mediated response) - a delayed response to microorganisms, tissue transplants, or chemicals that cause cellular inflammation; examples of this type of disorder include contact dermatitis, and Tuberculosis reactions (Mantoux test); type of antibodies involved: none

U

U.S. Electrical Standard - a standard for electrical current voltage and frequency used within the United States. These values are different for every country - in the U.S. they are 120 V for voltage and 60 Hz for frequency. This means that you will not be able to use an electrical appliance made for the U.S. in a country with a different electrical standard. Also, U.S. appliances use the so-called Type A (non-polarized, with two parallel flat prongs) and Type B (polarized, with two flat parallel prongs and a round grounding pin directly above them) plugs, which will not fit into, for example, European power outlets (where the Type C plugs with two round prongs are usually used).